Pseudomonas syringae pv. syringae, which causes the bacterial
apical necrosis of mango, produces the antimetabolite
mangotoxin. We report here the cloning, sequencing, and
identity analysis of a chromosomal region of 11.1 kb from
strain P. syringae pv. syringae UMAF0158, which is involved
in mangotoxin biosynthesis. This chromosomal region contains
six complete open reading frames (ORFs), including a
large gene (ORF5) with a modular architecture characteristic
of nonribosomal peptide synthetases (NRPS) named
mgoA. A Tn5 mutant disrupted in mgoA was defective in
mangotoxin production, revealing the involvement of the
putative NRPS gene in the biosynthesis of mangotoxin.
This derivative strain impaired in mangotoxin production
also showed a reduction in virulence as measured by necrotic
symptoms on tomato leaflets. Mangotoxin production
and virulence were restored fully in the NRPS mutant
by complementation with plasmid pCG2-6, which contains
an 11,103-bp chromosomal region cloned from the wildtype
strain P. syringae pv. syringae UMAF0158 that includes
the putative NPRS gene (mgoA). The results demonstrate
that mgoA has a role in the virulence of P. syringae pv.
syringae. The involvement of an NRPS in the production of
an antimetabolite toxin from P. syringae inhibiting ornithine
acetyltransferase activity is proposed.